When I try to upgrade the plugins I get this message and they do not upgrade.
An appropriate representation of the requested resource /moodle/mdeploy.php could not be found on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
I have moodle 2.5 and I think the certificate is ok.
I suspect that this is caused by something security related on your server. What is your server? Try checking the web server error log to see if there is more information.
It might be worth trying a different browser (or clearing the caches in your current one) just to eliminate any oddness there.
Check apache error logs for 406 errors. That error page is coming from Apache ... not even getting to Moodle.
According to other postings found via Google, error occurs due to Mod Security of apache.
The following about the same error for a word press site, but sounds like it might work for your situation:
Link above found via google:
However, if you are remotely hosted, check with service provider and inquire.
'spirit of sharing', Ken